Hot water heaters are commonly used to supply hot water to household users. In general, a hot water tank is connected to a pressurized water source. The water in the storage tank is heated by a source of energy, such as natural gas or electricity. When a user opens a faucet or fixture, the hot water is drawn from the tank into the system and cold water is supplied to the hot water tank.
Hot water heaters typically operate with little or no maintenance. However, the water stored in a water heater can corrode and weaken the structure of the storage tank causing a leak or rupture. Excessive pressure in the storage tank caused by extreme water temperature can also cause a rupture.
To minimize damage from water leakage, different types of shut off valves have been used to prevent the supply of water to the storage tank after the rupture occurs. Some of these devices are actuated by a leak detector provided below the water heater to detect the fluid that has leaked. Other shut off valves are actuated by the drop in pressure of the water in the storage tank of the hot water heater when a leak or rupture occurs. One such device is disclosed in U.S. Pat. No. 5,060,630 issued to Boals and incorporated herein by reference. The automatic shut off valve disclosed in this patent uses a diaphragm valve to control the supply of fluid to the storage tank of the hot water heater. When a leak or rupture occurs, the pressure from the storage tank drops to ambient pressure, causing the diaphragm to remain close and prevent the supply of water to the storage tank.
In this and other systems that rely upon a drop in water pressure to actuate the shut off valve, a false shut-off of the valve often occurs accidentally when no leakage has occurred. A false shut-off can occur with other pressure fluctuations in the storage tank that are not caused by a leak or rupture. For example, excessive drawing of cold water on the inlet side of the hot water tank during ordinary use could possibly cause a sufficient pressure drop in the supply line to actuate the automatic shut off valve, thereby causing the automatic shut off valve to lock up and prevent the supply of water to the hot water tank.
Accordingly, a need exists for an automatic fluid supply shut off valve system that is actuated by a pressure drop in a storage tank, such as a hot water heater, without accidentally locking up when pressure fluctuations that occur as a result of drawing fluid from the storage tank during ordinary use. A need also exists for a fluid monitoring device for use in a fluid supply shut off valve system to prevent unwanted false shut downs.